# File: AngularDifference.pm

package AngularDifference;

BEGIN {
    use Exporter;
    our @ISA = qw( Exporter );
    our @EXPORT = qw( &angdiff );
}

# compute the difference between angles $a and $b

sub angdiff($$) {
    my ($a, $b) = @_;
    return abs($a - $b) % 360;
}

1;

##</code><code>##

# File: AngularDifference.t

use AngularDifference;  # provides angdiff
use Test::More tests => 6;

# identical angles should have a diff of zero
is( angdiff(  0,  0),   # observed result
    0,                  # expected result
    "zero at 0"         # name of the test case
);                                           # case 1
is( angdiff( 90, 90),   0, "zero at 90" );   # case 2

# order of angles shouldn't matter to diff
is( angdiff(  0, 45),  45, "0,45 -> 45" );   # case 3
is( angdiff( 45,  0),  45, "45,0 -> 45" );   # case 4

# should return the smallest angle between
is( angdiff(  0,270),  90, "0,270 -> 90, not 270" );  # case 5

# multiples of 360-degrees shouldn't matter
my ($a,$b) = (360 * 2, 360 * 4);
is( angdiff($a,$b+23),23, "$a,$b+23 -> 23" );  # case 6

##</code><code>##

$ perl AngularDifference.t
1..6
ok 1 - zero at zero
ok 2 - zero at 90
ok 3 - 0,45 -> 45
ok 4 - 45,0 -> 45
not ok 5 - 0,270 -> 90, not 270
#     Failed test (AngularDifference.t at line 15)
#          got: '270'
#     expected: '90'
ok 6 - 720,1440+23 -> 23
# Looks like you failed 1 tests of 6.

##</code><code>##

sub angdiff($$) {
    my ($a, $b) = @_;
    return abs($a - $b) % 180;
}

##</code><code>##

$ perl AngularDifference.t
1..6
ok 1 - zero at zero
ok 2 - zero at 90
ok 3 - 0,45 -> 45
ok 4 - 45,0 -> 45
ok 5 - 0,270 -> 90, not 270
ok 6 - 720,1440+23 -> 23

##</code><code>##

is( angdiff( 90, 90),   0, "zero at 90" );   # case 2

##</code><code>##

# File: AngularDifference.l.t

use AngularDifference;
use Test::LectroTest;

Property {
    ##[ a <- Int, diff <- Int(range=>[-180,180]) ]##
    angdiff($a, $a + $diff) == abs($diff)
}, name => "angdiff holds to defn of angular difference";

##</code><code>##

    ##[ a <- Int, diff <- Int(range=>[-180,180]) ]##

##</code><code>##

    angdiff($a, $a + $diff) == abs($diff)

##</code><code>##

$ perl AngularDifference.l.t
1..1
not ok 1 - 'angdiff holds to defn of angular difference' falsified in 535 attempts
# Counterexample:
# $a = 148;
# $diff = 180;

##</code><code>##

When $a = 0

And $b is    The expected   And angdiff
             result is      returns
=========    ============   ===========
  150           150            150
  160           160            160
  170           170            170
  180           180              0  <-- Oops
  190           170             10  <-- Oops
  200           160             20  <-- Oops
  210           150             30  <-- Oops

##</code><code>##

sub angdiff($$) {
    my ($a, $b) = @_;
    my $delta = ($a - $b) % 360;
    return $delta > 180 ? 360 - $delta : $delta;
}

##</code><code>##

$ perl AngularDifference.l.t
1..1
ok 1 - 'angdiff holds to defn of angular difference' (1000 attempts)

##</code><code>##

Property {

    ##[ a <- Int, diff <- Int(range=>[-180,180]) ]##
 
    if    ($diff == 0)         { $tcon->label("zero") }
    elsif (abs($diff) <= 90)   { $tcon->label("1 to 90") }
    elsif (abs($diff) <= 180)  { $tcon->label("91 to 180") }
    elsif (abs($diff) <= 360)  { $tcon->label("181 to 360") }
    else                       { $tcon->label("> 360") }

    angdiff($a, $a + $diff) == abs($diff)

}, name => "angdiff holds to defn of angular difference";

##</code><code>##

1..1
ok 1 - 'angdiff holds to defn of angular difference' (1000 attempts)
#  58% 1 to 90
#  41% 91 to 180
#   0% zero

##</code><code>##

Property {

    ##[ a <- Int, n <- Int, diff <- Int(range=>[-180,180]) ]##
 
    my $b = $a + 360*$n + $diff;
    my $delta = abs($b - $a);

    if    ($delta == 0)    { $tcon->label("zero") }
    elsif ($delta <= 90)   { $tcon->label("1 to 90") }
    elsif ($delta <= 180)  { $tcon->label("91 to 180") }
    elsif ($delta <= 360)  { $tcon->label("181 to 360") }
    else                   { $tcon->label("> 360") }

    angdiff($a, $b) == abs($diff)

}, name => "angdiff holds to defn of angular difference";

##</code><code>##

1..1
ok 1 - 'angdiff holds to defn of angular difference' (1000 attempts)
#  98% > 360
#   0% 181 to 360
#   0% 1 to 90

##</code><code>##

n <- OneOf( Int(range=>[-1,1]), Int )

##</code><code>##

Property {

    ##[ a    <- Int,
        n    <- OneOf( Int(range=>[-1,1]), Int ),
        diff <- Int( range=>[-180,180] )  ]##
 
    my $b = $a + 360*$n + $diff;
    my $delta = abs($b - $a);

    if    ($delta == 0)    { $tcon->label("zero") }
    elsif ($delta <= 90)   { $tcon->label("1 to 90") }
    elsif ($delta <= 180)  { $tcon->label("91 to 180") }
    elsif ($delta <= 360)  { $tcon->label("181 to 360") }
    else                   { $tcon->label("> 360") }

    angdiff($a, $b) == abs($diff)

}, name => "angdiff holds to defn of angular difference";

##</code><code>##

1..1
ok 1 - 'angdiff holds to defn of angular difference' (1000 attempts)
#  67% > 360
#  17% 181 to 360
#   9% 1 to 90
#   6% 91 to 180
#   0% zero

##</code><code>##

n <- Frequency( [20,Int(range=>[-1,1])], [1,Int] )

##</code><code>##

1..1
ok 1 - 'angdiff holds to defn of angular difference' (1000 attempts)
#  37% > 360
#  32% 181 to 360
#  18% 1 to 90
#  10% 91 to 180
#   0% zero